1. Field of the Invention
This invention relates to a method for sterilizing semi-permeable membranes, and to the sterilized membranes. More particularly, it relates to a method of wet-heat sterilization of a semi-permeable membrane of regenerated cellulose, and to the semi-permeable membranes so sterilized.
2. Description of the Prior Art
Membranes with a variety of configurations such as hollow fiber, tubing and flat sheet have been widely employed in the treatment of fluids. Typical use for such membranes are in apparatus for purifying body fluids such as blood, which remove endogenous metabolites and exogenous toxins from such fluids. The artificial kidney is an apparatus designed to purify the blood with use of such a membrane and the ascitic fluid treating apparatus employs such a membrane for filtration and/or concentration of accumulated ascitic fluid.
The membranes in such medical apparatus must be used strictly under sterile conditions. The methods heretofore proposed for the sterilization of membranes include sterilization by immersion in formalin, sterilization with ethylene oxide gas and sterilization by gamma-ray radiation. The formalin immersion and ethylene oxide gas sterilization techniques have been widely practiced. However, it has been found that the use of membranes sterilized by such known methods results in the absorption of residual formalin or ethylene oxide into the body fluids and, or repeated use of such membranes, such substances gradually accumulate in the body until, finally, a harmful level can be attained. Under the circumstances, the aforementioned radiation sterilization technique has been preferred, but the use of radiation has a risk of health hazards and, hence, requires complicated and costly equipment, thus presenting its own problems to be solved before such a technique may be well established. It is for this reason that a sterilizing technique safe to patients has long been desired and sought after.